“It’s totally unjust,” he says. “It’s not fair to the maple-syrup producers. It’s not fair to the consumers either.”

For the nation’s largest maple syrup producer, nothing less than a pillar of the state’s reputation is at stake.

“This issue gets the core of Vermont’s brand,” says Anson Tebbetts, the state’s Secretary of Agriculture, Food and Markets, whose family farm has a maple sugar house and whose father was once pictured on a maple syrup can. “We’ve taken tremendous pride in the fact that Vermonters produce a pure product that has no additives. A label stuck on it saying it has added sugar would just add confusion.”

The FDA’s new rule says its definition of added sugars “includes sugars that are either added during the processing of foods, or are packaged as such, and include sugars (free, mono- and disaccharides), sugars from syrups and honey.”

By the government’s definition, pure honey and maple syrup themselves are added sugars because, like table sugar or high-fructose corn syrup, they add calories to the diet but few or no nutrients.

Maple syrup and honey makers worry the label might lead consumers to think they’ve added sugar. “We have never added sugar to pure maple syrup,” says Mr. Folino, who with his wife owns Hillsboro Sugarworks in Starksboro, Vt. They are among producers asking the FDA to exempt them or change the label.

More than 3,000 comments poured in to the FDA in recent weeks on the new rule and a proposed compromise—many at the urging of Vermont Attorney General T.J. Donovan, who directed Vermonters to a webpage titled “100% Pure: Maple and Democracy” with a link to submit comments to the agency.

“Stop trying to fix things that don’t need fixing,” wrote a Vermont commenter.

“Are you people insane?” wrote one from Indiana. “Your proposed rule will completely undermine consumers’ faith in the purity of honey and maple syrup.”

FDA Commissioner Scott Gottlieb, who has said he makes maple syrup at home, tweeted on Thursday that the agency has “heard the concerns,” and “will advance a new approach to how we treat maple syrup and honey under the new nutrition facts label.” An FDA spokeswoman declined to comment on what that approach might be.